Vitamin K took its name from the Danish word “Koagulation”, and its discoverer received the Nobel Prize for it. In Zielona Góra, we ferment soybeans with the bacterium Bacillus subtilis var. natto, which during fermentation produces menaquinone-7 (MK-7), a form of vitamin K2 present in our natto in high concentration. I have gathered here what is known for certain: where the name vitamin K came from, how its forms K1, MK-4 and MK-7 differ, and what the scientific literature says about MK-7 from natto.
⚠️ Are you taking anticoagulant medication (for example acenocoumarol or warfarin)? Natto is one of the richest natural sources of vitamin K, which may affect how these medicines work. Consult your diet and supplements with a doctor. See the important legal and medical information.
In short
- Vitamin K2 MK-7 is a long-chain menaquinone, a form of vitamin K that in nature forms mainly during bacterial fermentation, just as in our natto.
- Vitamin K contributes to normal blood clotting and to the maintenance of normal bones. These are the two authorised health claims for vitamin K (Regulation (EU) 432/2012).
- The name “vitamin K” comes from the Danish word “Koagulation”, because the first described function of this vitamin was blood clotting.
- MK-7 differs from the K1 and MK-4 forms by the length of its side chain, which translates into a longer residence time in the blood.
- Natto is one of the richest natural dietary sources of MK-7.
Where the name vitamin K came from
Vitamin K was discovered in the 1930s by Danish biochemist Henrik Dam, who was studying blood clotting in chickens fed a fat-free diet. He named it after the Danish word “Koagulation”, meaning coagulation, and that is how it has remained to this day, in almost all languages, even though the letter “K” in most of them no longer evokes the Danish root. For discovering vitamin K and its role in blood clotting, Dam received the Nobel Prize in Physiology or Medicine in 1943.
Three forms of vitamin K: K1, MK-4 and MK-7
Vitamin K is not a single compound but a family of related molecules. Phylloquinone, or vitamin K1, is found mainly in green leafy vegetables, for example in spinach or kale. Menaquinones, or vitamin K2, differ in the length of their side chain, hence the designations MK-4, MK-7 and others. MK-4 is found mainly in animal products, while MK-7, the long-chain menaquinone, forms in nature primarily where bacterial fermentation takes place, for example when Bacillus subtilis var. natto ferments soybeans. That is exactly how MK-7 appears in our natto.
How vitamin K works in the body
Vitamin K acts as a cofactor for an enzyme that activates vitamin K-dependent proteins. Two of them are osteocalcin and the protein MGP (Matrix Gla Protein). Osteocalcin participates in binding calcium in the bone matrix, and MGP, present among other places in the walls of blood vessels, is analysed in the literature in the context of calcium metabolism. These mechanisms are the subject of ongoing research and remain a description of a biochemical process.
What research says about natto and vitamin K2
Natto and the vitamin K2 MK-7 it contains have been the subject of scientific research. Below we describe what was observed in selected studies, together with a note on how cautiously they should be interpreted.
- Consumption of natto was associated with an increase in the level of MK-7 and carboxylated osteocalcin in the blood (Tsukamoto, 2000).
- In an observational study of the Japanese Takayama cohort, higher natto consumption was associated with slower bone mass loss in postmenopausal women (Ikeda, 2006). This is a correlation, not proof of a causal relationship.
- In a three-year study of MK-7 supplementation in healthy postmenopausal women, changes in markers of vitamin K status and bone metabolism parameters were observed (Knapen, 2013).
Observational studies describe the co-occurrence of phenomena, not a cause-and-effect relationship, and individual intervention studies require confirmation in larger, independent trials. The above results do not justify attributing any additional health effect to natto beyond what vitamin K describes as a nutrient.
Bioavailability of MK-7 from natto
Forms of vitamin K differ not only in structure but also in how long they remain in the blood. MK-7 has a longer plasma half-life than MK-4, which means its level after consumption is more stable over time. This is a pharmacokinetic property of the molecule, described in studies on the absorption of different forms of vitamin K, and not an additional health effect. In practice this means that natural sources of MK-7, such as fresh natto, provide a form of vitamin K that remains active in the body for a long time.
Vitamin K2 MK-7 in our natto
You will find MK-7 in every one of our natto products, because it is a natural product of fermentation by the bacterium Bacillus subtilis var. natto. Fresh natto tells the most about it: soybeans right after fermentation, without further processing. We produce it in Zielona Góra from certified organic soybeans.
See our fresh natto with natural K2 MK-7
Safety and precautions
Natto is a food safe for most healthy people. Due to its high vitamin K content, in a few situations it is worth exercising particular caution.
This applies above all to people taking anticoagulant medication from the vitamin K antagonist group (for example warfarin or acenocoumarol), because vitamin K may affect how these medicines work. Consult your doctor about consuming natto and vitamin K2 supplements. Caution is also advisable during pregnancy and breastfeeding and when taking other medicines regularly; in such situations the decision to increase vitamin K2 intake is best discussed with a doctor. Natto contains soy, so it is not intended for people with a soy allergy. A food supplement or any food product does not replace a varied diet and a healthy lifestyle.
Summary
Vitamin K2 MK-7 is a long-chain menaquinone whose name and history go back to a Danish discovery almost a hundred years ago. Natto, thanks to fermentation by the bacterium Bacillus subtilis var. natto, is one of its richest natural dietary sources, and the MK-7 form is distinguished by a longer residence time in the blood than K1 or MK-4. Vitamin K contributes to normal blood clotting and to the maintenance of normal bones, and natto is worth treating as part of a varied diet.
Frequently asked questions
Why is vitamin K2 MK-7 from natto well absorbed?
It is a natural form of vitamin K2 that forms mainly during bacterial fermentation in nature and remains in the blood longer than the K1 form. The longer plasma half-life is one of the characteristics that distinguish MK-7 from other forms of vitamin K.
Which health claims for vitamin K are permitted in the European Union?
Two: vitamin K contributes to normal blood clotting and to the maintenance of normal bones. These are the only authorised health claims for vitamin K, so we do not attribute to natto or the MK-7 form any effect beyond them.
Is an MK-7 supplement the same as vitamin K2 from natto?
Chemically it is the same compound. Natto as a food additionally provides plant protein, dietary fibre and live cultures of fermentation bacteria, which a capsule alone does not contain.
Can everyone consume vitamin K2 from natto?
For most healthy people natto is an ordinary food. The exception is people taking anticoagulant medication from the vitamin K antagonist group, who should exercise caution and consult their doctor about consuming it.
Sources
- Tsukamoto Y. et al., Intake of fermented soybean (natto) increases circulating vitamin K2 (menaquinone-7), J Bone Miner Metab, 2000. pubmed.ncbi.nlm.nih.gov/10874601
- Ikeda Y. et al., Intake of fermented soybeans, natto, is associated with reduced bone loss in postmenopausal women, J Nutr, 2006. pubmed.ncbi.nlm.nih.gov/16614424
- Knapen M.H.J. et al., Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women, Osteoporos Int, 2013. pubmed.ncbi.nlm.nih.gov/23525894
- Regulation (EC) No 1924/2006 and Regulation (EU) No 432/2012. EU Register of Nutrition and Health Claims (European Commission).
Legal and medical note. This article is educational and does not replace the advice of a doctor or pharmacist. Vitamin K has two authorised health claims in the European Union (Regulation (EC) 1924/2006, Regulation (EU) 432/2012): it contributes to normal blood clotting and to the maintenance of normal bones. Beyond these two claims we do not attribute any additional health effect to natto or vitamin K2 MK-7, and a food supplement is not a medicine and does not replace a varied diet. Full information is on the Legal and medical information page.
